Brake



April 1, 1941 L. R. WILLIAMSON 2.237.170 r a BRAKE med march s1, 1939 s sheets-sheet 1 Fig. Z B 7,4m@ 3 ya? l Arr RNEY.

l. R WILLIAMSON 2,237,170

Ap l, 1941.

BRAK E Filed March 31, 1939 6 3A Sheets-Sheet 2 H 13 /vmce :6. 7417.

ATTORNEY.

April 1;,1941- l. R WILLIAMSON BRAKE Filed March 31, 1939 6 Sheets-Sheet fof/ A INVNTOR BY Ae/ew M/.Lmmsa/Y 6 so 'YY 9/ M 71mm.

L. R. WILLIAMSON Y 2,237,170

BRAKE.' i v Filed :aaron 51, 1939 6 sheetsffsnemA 4 INVENTOR 'l 6 your I April l, 1941- l. R WILLIAMSON 2.237.170

BRAK E Filed March 31, 1939 6 Sheets-Sheet 5 BRAKE 6 *Sheetsasheet s R. WILLIAMSON Filed March 31, 1939 in which used..

Patented Apr. l, 1941 2,237,170 BRAKE Inrkin R. Williamson, Brooklyn, N. Y., assignor to E. W. Bliss Company, Brooklyn, N. Y., a corporation of Delaware Application March 31, 1939, Serial No. 265,238

19 Claims. (Cl. 153-21) 'I'his invention relates to a metal bending brake, and more particularly to an improved brake of clean and simple' construction which may be easily assembled at the point of use.

Metal bending brakes constructed of steel plates are well known in the art, The use of metal plates in constructing such machinery has, however, in the past entailed structural objections due to the bending strains to which the frame plates were subjected; a diiliculty which could' be eliminated where heavy castings were employed and weight was no consideration.

It has been the general object o! my invention to devise an improved and simplified brake which is more elcient than the type heretofore used Vand which is economical to manufacture and simple-to construct.

Generally, my brake comprises end plates, a bed plate and a ram. Suitable shafts and gears are carried by the fixed parts to provide a drive for reciprocating the ram. The ram is mounted to transmit thrust imposed on it to the supporting frame in the plane of the endplates, thus` preventing their deformation through bending. A fluid clutch and brake is employed to connectand disconnect the source of power and this is characterized by a double or two stage application of pressure during engagement of the clutch.

Thus the initial -clutch engaging pressure is intional pressure which acts to prevent slippage of the clutch plates.

An electric system is provided to control the application of duid to the clutch and brake and this system includes safety switches and an emergency stop to. prevent damage to the parts if the machine is over-loaded. The machine may be adjusted for intermittent or continuous operation.

lI further provide safety mechanism to protect the end plates against over-loading, which mechanism acts, if the plates are unduly stressed, to release the clutch and stop the machine before permanent injury is done to the parts. To the accomplishment of the foregoing-and related ends', said invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims; the annexed drawings and the following description-setting 'forth in detail certain mechanism embodying theinvention, such disclosed means constituting,

Fig. 8 is a perspective of the drive system of Y the brake;

Fig. 9 is a wiring diagramshowing the elec-I trical connections of the parts;

Fig. l0 shows the iiuid system by which the clutch is engaged.

Fig. 11 is a section through Fig. 10, as indicated by the line Il-II thereon;

Fig. 12 is a detail of the safety mechanism, as shown by the line i2-I2 on Fig. 4; and

Figl 13 is a detail of the fluid system controls.

Referring now particularly to Figs. 1 through 4, my brake comprises a pair of end plates 20 and 2l, which are bolted as at 23 to a suitable support carried by the foundation on which, the machine is mounted. The forward portion of each plate Ais provided at 2l with outwardly extending shoulders on which is hung a bed 25. Interposed between the bed and shoulders vis a strip 26 made of hardened steel to absorb the shock and wear between the parts and to transmit the load from the bed to the shoulders. The bed is prevented from falling from the shoulders by bolts 28 which pass into the adjacent part of the end plates. To `further reinforce the bed and end plates,

Y bracing webs 30 are provided which are trianguhowever, but: oneof various mechanical forms the principle of the invention may be In said annexed a u lar in'4 shape and secured alongvthe sides to the bed and respective end plates in a position parallel to the foundation. At the upper part of the end plates an angle member 32 is secured which extends across the brake and is fastened at its ends to each plate to reinforce the same and pro-y vide a solid non-yielding frame construction.

At the forward face of the plates 20 and '2| are ways 34 which` slidingly guide a ram 35 mounted for reciprocating mov'ement from and toward the bed 25 to bend a piece of -metal positioned therebetween. The ram and the bed are provided with means for securing dies thereto, such as indicated bythe dot and dash lines in Fig. 4.

The ram is reciprocated by means of a' pair of pitmans and eccentrics shownin Fig. '1. Adjaincludes an upper sleeve 45 which threadingly receives an'd holds the lower part in a bushing 41. Each sleeve part is formed at its upper end as at 49 to receive an eccentric 50 by which each pitman acts to move the ram supported thereby up and down in the ways 34- e Bifurcated supports 52 are bolted at 53 to each of the end plates 20 and 2| which are correspondingly recessed to receive them. Each support fits into the recessed part of the end plates, as shown in Fig. 3, to provide ample clearance for the respective pitmans and eccentrics. The construction just described allows all of the force applied against the ram tobe applied in a line coinciding with the plane of each end(l plate and thus the tendency of the frame to bend in operation is largely eliminated. Each bifurcated support receives and rotatably supports a stub shaft 55, which in turn carries the eccentrics 50 heretofore described. On the exterior portion of each stub shaft is mounted a bull gear 51 by which the eccentric is rotated and the ram raised and lowered as hereafter described.

In setting up the machine for operation with a given p air of dies it is frequently' necessary to adjust the position of the ram with respect to the bed. This is accomplished by turning the lower pitman parts 40 into or out of the sleeve 41. To this end I provide a motor 60 mounted on the ram structure which drives a telescoping shaft 52, extending across the ram and connecting at each end into the pitman construction at the ends of the ram. A pair of worms are carried at the ends of the shaft and each engages respectively With a Worm wheel 63, keyed to each pitman ele- I ment 40. Thus, depending on the direction in which the part 40 is rotated and the ram is raised or lowered with regard to the upper pitman structure 45 to adjust the ram with respect to the bed.

The eccentrics are rotated and the ram actuated by the driving mechanism shown in Fig. 8. In this figure the pitmans are 'shown as hung on the eccentrics 50, which in turn 'are rotatably carried with the bull gears 51. A back shaft 55 extends fromone side of the tool to the other and is journaled in the end plates 20 and 2|, as shown and brake unit and is provided with belt grooves to receive va series of belts 18 driven fromA the pulley 19 mounted on the shaftof a motor 00.

The motor in turn is carried on a bracket I2v (Fig. 3) which is pivoted to the end plate 20 at 93 and provided with an adjustment at 84, by which tension in the belt may be varied.

.in Figs. 3 and 4, This shaft carries a pair of .pinions 61 which engages with respective bull supports a clutch ring 84 keyed thereto for sliding movement axiallyon the shaft. The ring .is normally drawn to the left side of Fig. 6 and the clutch disengaged by a plurality of studs 85 carried by the ring which carry compression springs 01 interposed between the hub and nuts 08 at the ends of the studs.

To shift the ring to the right and engage the clutch, four pistons are provided which are slidable in cylinders 9| in the hub. The cylinders are capped as at 88. Pins 94 extend through the hub and are engaged bythe pistons to transmit the force applied against the pistons to the ring 84 to shift the ring to the right (Fig. 6) against the force of the springs 01. Fluid to actuate the pistons is brought under pressure to the cylinders by anA axial passage 95 in the shaft 10 and related passages through the hub 82. The shaft 10 terminates in a seal |00 of the conventional type by which fluid is applied to the rotating shaft and cylinders from a stationary xture |02 mounted at I 04 on the end plate 20. A removable end bearing member |05 is bolted into the end plate 20 and supports ball bearings which in turn carry the shaft.

To change belts on the flywheel the unit |05 is bodily removed from the machine and the flywheel is supported against falling by supporting studs |01, which may be threadingly advanced upwardly against the flange of the wheel. It is then possible to remove the belts and replace them with new ones by passing the belts between the shaft and the end plate and without completely dismantling the machine, as has heretofore been customary. A

The actual engagement of the clutch and shaft iseffected by friction disks 4I|0 carried by the flywheel and axially slidable thereon. 'I'he brake is engaged by a second set of friction disks slidably carried by the clutch housing I I2 on a radial plate I I4 and engaged by ring B4. When the clutch ring 84 is shifted to the left (Fig. 6) by the springs 81 it clamps the friction member I|4 between itself and a ring 5 integral with the hub to lock the shaft 10 against rotation. On the other hand, as the ring 84 is moved to the right by admitting uid to the cylinder 9| the clutch element IIO, carried by the flywheel, is clamped between the ring 84 and a hub flange I I 8 to couple the'ilywheel and the shaft as a rotative unit and drive the brake To compensate for wear in the friction surfaces the ring ||5 may be adjusted axially of the hub and thenkeyed as at |20 to retainthe parts in position.

Fluid, as loil, under pressure, to actuate the -'pistons 90, is supplied through the mechanism shown in Figs. 3, l0 and 11. This system includes two pumping units by which an initial pressure is rst applied to engage the clutch and after such engagement an additional higher pressure is applied which remains in force during the operating stroke of the ram.

The first or low pressure pump is mounted on r"theendplate 20 (Fig. 3), as generally indicated The construction of the clutch and brake is. l

best shown in Figs. 5 and 6. As there shown the flywheel 11 is idly carried'on the clutch shaft 10.

at |25 and includes therewith an electric torque meter |21 and magnetic brake mb, by which the pump is driven and controlled. A shaft from the motor carries a pinion |28 driving a gear |29 on the camshaft |30 journaled in the housing |25 in ball bearings I3I.

The pump proper includes a cylinder |33 in the casing which receives apiston |35,`normally held in an upward position by a compression spring |31. The entire piston and cylinder unit is re- Fix'edly carried on the shaft is a hub 02 which 7.5 movable through the under side of the pump casr ing by removing the bolts |38. A cam |40 is keyed at |42 to the shaft |30 and as the shaft is rotated by the torque motor the cam surface pushes the piston |35 downwardly by bearing against a ball bearing cam follower |45, rotatably mounted in a slot in the piston. The torque motor becomes stalled when it has turned the cam |40 far enough to apply a fluid pressure equal to' the power of the motor. The period of rotation of the motor is so short that before the workman releases the foot pedal hereafter described the motor will have done its work. When the pedal is released the current to the motor is cut off and the brake is set to hold the pump in an active position.

Piping |41 leads'from the cylinder |33 through a shut-01T valve |48 and a pipe line 50 to the stationary intake |02 to the shaft 10 (Fig ,6). The pressure established as just described actuates the clutch pistons 90 and engage the clutch to rotate the shaft 10, which in turn drives the gear train of Fig. 8, including the shaft 65 and eccentrics 50.

A second pump to apply increased Ioperating pressure to the system during the work stroke of the machine is actuated by' the right hand eccentric 50. The second pressure pump, best shown in Figs. 1 and 10, comprises a casing |55,

bolted at |56 to the bifurcated member 52. Part of the casing encircles the end of the shaft 55, on which is mounted a cam plate |58 rotatable therewith and shaped as shown in Fig. 10. A cylinder |60 is formed in the casing and receives a piston unit formed of two parts |62 and |64 normally held apar't by a compression spring |65. The amount these parts can separate may be adjjusted and is limited by a bolt |61. The lower piston part |62 carries a follower |10 which rides against the cam |58.

A small high pressure cylinder block is bolted to the top of the casing |55 by bolts |12 and receives an extension |14 of the piston unit |64 ofreduced diameter. This cylinder communicates through a. check valve |15 with piping |11 Vcomincreased operating pressure to vthe clutch plates which augments the pressure already established by the pump |25.

l The high pressure pump tained safety mechanism to preventfapplyingan unsafe pressure to the iiuid system. To this end the spring |65 is of a predetermined strength to be compressed when the highest desired operating pressure is attained in the fluid system. When this point is reached the portion |64 of the piston unit will remain stationary because the .uid pressure isgreater than the spring strength of the spring |65. As a result, the portlon|62 of the piston unit may reciprocate under the inuence of the cam |58, although no increased operating pressure will be applied to the system because the part |1 4will be stationary and the y excess oil in the system passes back to the housing through the passage |83 in the cylinder wall which is exposed on the' up stroke of the piston |35. As soon as the piston starts d own this opening is cut off. To supply oil to the casing |25 a removable plug |85 is provided.

Small .quantities of oil must be added from time to time to the high pressure cylinder block. This is accomplished through piping |81 connecting the housing and the piping through a check valve |88. Normallyl the valve |88 is held closed.

-However, as the amount of oil in the cylinder drops below the required amount the suction created opens the valve and draws oil into the l cylinder.

To energize the motor |21 and start the operation of the brake theq electric system shown in the wiring diagram of Fig. 9 and the foot pedal mechanismof Fig. 13 is provided. A foot treadle' |90 is pivotally carried at |9| by a bracket |92 bolted to -the machine frame. An inner end 'tem through piston |35. The system, includes control mechanism and safety devices to prevent overloading or damaging of the parts.

Referring to the wiring diagram in Fig. 9, the motor |21 and the magnetic brake |21h are alternately connected to assource of power 205 by a forward switch 201 or a reversing switch 208.

The switches in turn are actuated by electric controls 209 and 2|0, respectively. When the switch 200 is closed current passes from the line 205 to actuate the mechanism 209 and close the forward switch 201, thereby energizing the motor |21 to engage the clutch mechanism as heretol fore described as long as the operator keeps his l municating withthe piping |50 which leads to the clutch. This. mechanism functions to apply an includes a self-conl 'scended andhas almost completed its upward. stroke, at which time the motor |21 isreversed by a limit switch 2|2 (Fig. '1) actuated by a lug `foot on the treadle.

When he releases the treadle the switch 200opens and the forward circuit is broken, cutting olf the supply of current. This allows thebrake |21b which is spring actuated, to lock and hold the cam |40 in the position then attained.

When the brake nis intermittently operated the clutch remains engaged untilv the ram has de- 2|4 mounted on the pitman member 4,5. When this switch is energized (Fig. 9) the mechanism 2|0 is actuated to reverse the motor and back oif the cam |40, releasing the pressure in the system. The mechanism is 'so arranged that-they brake is stopped, while the cam follower |10 (Fig. 10) is on the portion |58 of' least diameter. The inertia of the parts .will-carry the ram and pitman past the point closing switch 2|2f'and thus allow the switch Ato open', positioning the electrical circuit for operation through a second cycle. A limit-switchv 21|3, operated by an adjustable 'arml 2|5 on l'shaft |30 is providedV and is opened each time the torque motor returns the cam |40 to the position of Fig. 10. Thus, if the switch 2|2 is not openedthis latter switch will act to open and release the reversing switch 208. To provide a' continuouslyV operating tool a switch 2|5 is provided whichif open prevents the energizingof the switch 208 which reverses the motor. When the switch is closed, as shown in Fig. 9, the mechanism is established for intermittent operation. A manual emergency switch 2| 1, also mounted on the side of the machine in Fig. 3, is provided to quickly reverse the motor and release the clutch pressure to stop the operation of the tool. I'he switch is normally in the position shown Ain Fig. 9, and is shifted to engage the lower contacts and reverse the motor |21 to stop the brake in an emergency.

To prevent undue stressing of the end plates 20 and 2|. safety mechanism, as shown in Figs. 3, 4.and 12, includirm a pair of safety switches 220 and 222, is provided. This mechanism comprises two units each consisting Aof a strap 225 pinned at 226 to the lower portion of a respective. end plate. Each strap passes upwardly through guides 228 carried by the plate and is curved as indicated to avoid interference with the parts of the press and each strap' terminates adjacent the top of a respective end plate. Welded at the top of each strap (Fig. 12) is a bracket 230 which carries a very sensitive limit switch 220 or 222, as

the case may be, connected into the system as indicated on the wiring diagram of Fig. 9. Threadingly carried in the top of each plate and adapted to underlie the actuating member of each switch is a bolt 232 adjustably locked in position by a lock nut 234.

Thesafety mechanism functions to reverse the supply of current to the motor |21 and remove the load from the tool if either end plate is unduly strained. In other words, if an excessive load is applied at the dies there is a tendency for the plates 20 or 2| to stretch beyond their elastic or safe limits. The mechanism is so adjusted that before this limit is reached the elongation of either plate will have actuated the corresponding limit switch and closed the reversing circuit to the motor |21, thus backing on the cam M0 (Fig. 10) and disengaging the clutch and applying the brake as heretofore described.

To inch the tool in setting dies or the like it is desirable to provide manual means to apply small increments of pressure to the fluid system and closely control the position of the ram, accomplish this by mechanism best shown in Figs. 3 and 13. As there shown I provide a bracket 240 bolted to the end plate 20 and carry ing a cylinder 242, in which slides a piston 244. The Ycylinder communicates through piping 245 with the general fluid system, as shown in Fig. 10.

A hand` lever 241 is pivoted at 248 to the bracket 2.40. Its movement to the right (Fig. V13) is limited by a pin 250 and when the lever is moved to the left pressure is applied to the system by the piston 244 to lightly engage the clutch and turnv over the parts. The clutch is disengaged by simply shifting the lever in the other direction.

The amount of pressure applied is just enough to engage the parts and not enough to prevent stalling of the tool by slippage of the clutch plates if any appreciable load is applied to the ram. With this mechanism it is thus possible to safely inch the ram during adjustmentvof the ram and the dies for set-up purposes before beginning production operation of the machine.l The hand lever may of course be applied to actuate the parts at any tim-e where no appreciable hold is to be applied to the tool.

- Operaton anto the werking position desired at the bottom of the stroke, at which time nal adjustment for ram stroke is made. This inching movement is had by manual manipulation of hand lever 241, which actuates piston 244 and applies pressure to the fluid in pipes 245, 50 and |02 to the clutch 15.

The stroke of the ram is constant and is predetermined by the eccentric 50, but the effective ram position at a given instant can be raised or lowered by energizing motor 50, which elongates or shortens the eifective length of the pitman. Thus the end of the stroke can be adjustedwith respect to thebed 25.

A sheet to be worked is placed in position upon the lower die and the foot treadle- 90 is depressed, releasing the magnetic brake |21b and energizing motor |21, which moves piston and applies pressure to fluid in piping |41, and |02 to engage clutch 15. When this pressure builds up to a predetermined amount, the motor |21 stalls, but it remains energized until treadle |50 is released,

at which time brake |21b locks the motor against rotation, causing the pressure to remain 'constant at a built-up level.

When ram 35 hastravelled downwardly so that it is about to contact the sheet, the cam moves piston |54, thereby increasing the pressure in piping |11, |50 and |02, causing an increase in the engaging pressure of the friction surfaces oi' the clutch 15. Thus, when the die which is carried by the ram contacts the article, the clutch is less apt to slip and greater forces can be transf mitted by the ram.

If these forces become so great or are so directed that one of the side plates 20 or 2| is unduly stressed and stretched, one or both of the safety switches 220 or 222 is activated to release brake |21b and reverse the direction of rotation of motor 21 releasing piston |35. Thus, the stresses in side plates v2li or 2| is relieved before damage is done, as by stretching beyond the elastic limit.

When the ram reaches its lowermost position, cam |58 has rotated so as to partially release the pressure engaging the clutch 15.

The clutch remains in engagement, however,

until the ram is almost to the top of its stroke, at-

which time switch 2|2 will act to release brake |21b and reverse motor |21 to completely release clutch 15, at such time that the ram, due to inertia, will coast toits uppermost position and the ram cycle is completed.

lWhen motor |21 is reversed, it will be stopped by limit switch 2|3', so that cam |40 is in its invention may be employed instead of the one explained, change being made as regards the means and the stepsvherein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out 'and distinctly claim as my invention: s y

1. In a. machine tool. a fixed frame comprising relatively thin plates, a movable work member adapted to cooperate with said xed frame to perform a work operation and thereby stress said plates, power means to drive said work member,

' and means operative automatically whenever the engage stress in one of said plates is beyond a predetermined point to prevent said power means from driving said work member.

2. In a machine tool, a frame, a movable slide carried thereby, power means to drive said slide, a clutch interposed between said power means and said slide, frame members to receive the stress resultant from the work stroke of said slide,

and means operative automatically consequentA upon straining one of said frame members beyond a predetermined point to disengage said clutch.

3. In a machine tool, a frame, a movable lslide carried thereby, power means to drive said slide,

a clutch interposed between said power means and said slide, frame members to receive the stress resultant from the work stroke of said slide, means associated with one of said frame members responsive solely to the deformation of one of said frame members due to the stress transmitted thereto and means operative by said responsive means to disengage said clutch consequent upon a predetermined degree of deformation in one of said frame members.

4. In a machine tool of the class described, a

vframe including a bed, a ram movably carried by holder, iiuid pressure means to actuate said clutch, manual means to`A apply pressure to said pressure means to engagesaid clutch and power means to apply pressure to said pressing means independently of said manual means to engage saisLclutch.

6. In a machine tool of the class described, a

provide a frame structure, a pair of bifurcated supports integral with said end plates, eccentrics carried in said supports, pitman members carried by said eccentrics between the bifurcations of said supports and a ram carried by said pitman members.

10. In a machine tool of the class described, a frame comprising a pair of end plates, a slide reciprocably carried by said end plates adjacent the forward edge thereof, said plates having recesses at the forward portions thereof above said slide, a. bifurcated support mounted in each recessed portion, flanges on each support to engage the opposing faces of a respective plate adjacent said recess, means to rigidly secure said flanges to the respective plate, an eccentric mounted in each support, a pitman carried by each eccentric between the bifurcations of said respective supports and operatively connected to said slide.

l1. In a machine tool of the class described, a pair of spaced end plates, a bed plate secured to .the forward ,part of said end plates 'to provide a frame structure, a ram slidably carried by said end plates, a pair of eccentrics mounted adjacent respective end plates, power means to drive said machine including a fluid operated clutch, a pump unit carried by said frame adjacent an eccentric to apply fluid pressure to said clutch and a cam rotatable with said eccentric to drive said pu-Inp- I 12. In a machine tool of the class described, a pair of spaced lend plates, a bed plate secured to the forward part of said end plates to provide a frame structure, a `ram slidably carried by said Aposed between said power means and said tool frame including a bed,`a ram movably carried by said frame, power means to drive said ram, a clutch interposed between said ,ram a'nd said power means,.means to engage said clutch to drive said ram and a second means operative additional to said first means to apply an increased Y operating pressure to said clutch engaging means. 7. In a machine tool ofthe class described, a frame, a ram movably carried by said frame,

power means to drive said ram, a clutch inter.

posed between said ram and said power means,

means to apply an initial engaging force to said I clutch to begin the movement of said ram and means operative after said ram has attained a predetermined position to apply an increased enperforming stroke of said ram.

8. In a press brake or the like, a stationary frame, a ram slidably carried by said frame, a

pair of eccentrics in said frame adjacent the endsv gaging force to said clutch during the work end plates, a pair of eccentrics mounted adjacent respective end plates, power .meansto drive said machine including a fluid operated clutch, a pump and operating means therefor to apply 'fluid pressure to said 'clutch to establish a drive to said machine, a second pump unit carried by said frame adjacent an eccentric thereof to ap- 1 ply further fluid pressure to said clutch and a cam rotatable with said eccentric to drive said second pump unit.

13. In a machine tool of the class described, a

pair of end plates, a ram slidable with respectthereto, a bifurcated support carried byV each end plate with theregion between the bifurcaably mounted in' the bifurcationsof each support, a pitman member carried by each eccentric, a

-ball and socket connection in each end of said ram in alignment with said pitmans respectively and means to retain respective .pitmans in said socket connection.

14. In a machine tool of the class described, a pair. of end plates, a` ram slidable with respect thereto, a bifurcated support carried by each end plate with the region between the bifurcations in alignment with the general plane of said plates respectively, an` eccentric member rotatably mounted in the bifurcations of each support, a hollow pitman member carriedr by each eccentric, a ball and socketl connection in said ram in alignment with each eccentric, rotatable pitman members supported at one end in said sockets and at the other end threadingly received in respective `hollow members and rotatable to adjust the disalignment with the general plane of said plates.

respectively, an eccentric member rotatably mounted in the bifurcations of each support, a pitman member carried by each eccentric, a ball and socket connection interposed between said pitman member and said ram in alignment with each eccentric and means to vary the dis-- tance between a point'on said ram and the axes of said eccentrics.

16. In a machine tool of the class described, a

chronously extend said pitman members.

17. In a machine tool of the class described, a

pair of flat end plates with outstanding shoulders formed at the lower forward edges thereof, a bed plate with recesses extending inwardly from the end edges thereof to interlock with said shoulders respectively and corner brace members secured to the inner face of said bed and 'said end plates respectively to form a unit of said bed and said end plates.' l

18. In a machine tool of the class described, a pair of frame members, a shaft extending therebetween, a drive pulley on said shaft between said frame members, a removable shaft bearing in one frame member of such configuration that, when removed, an opening is provided between the shaft and said last-named frame member and means to suspend the shait in said opening to permit replacement of a continuous belt on said pulley through said opening.

19. In a device of the character described, a frame having uprights, aA ram adapted to cooperate therewith to perform a working operation and thereby strain said uprights, power means to drive said ram and means for preventn ing said power means from driving said ram, said means being automatically operative solely upon said strain reaching a predetermined limit.

LARKIN R. WILLIAMSON. 

